Title:What can the mid-Tertiary unconformity tell us about deformation and erosion in the Nevadaplano?

AbstractThe hinterland of the Sevier orogenic belt in Nevada and western Utah has been interpreted as an ancient, high-elevation orogenic plateau, or ‘Nevadaplano’ that extensionally collapsed during Tertiary time. To illustrate the pre-extensional structural relief of this region, a new paleogeologic (or ‘subcrop’) map showing the distribution of Neoproterozoic to Triassic sedimentary rocks exposed beneath a regional Paleogene unconformity is presented. In addition, using published isopach maps of depositional thickness of Neoproterozoic to Triassic rocks, the paleogeologic map has been converted into a map that contours the thickness of rock eroded between the top of the Triassic section and the Paleogene subcrop level, and therefore illustrates magnitudes and spatial patterns of synorogenic erosional exhumation.

Several implications of these datasets are explored, including constraints on the map patterns of regional-scale contractional structures, and correlations between hinterland structures and structures in the frontal Sevier thrust belt. Interestingly, much of the hinterland region exhibits low (ca. 2 km) structural relief, indicating that the majority of regionally-distributed, surface-breaking normal faulting that dismembered the orogenic highland and produced the high structural relief observed today had to be post-Oligocene. Finally, some similarities and differences between the Sevier and Central Andean orogenic plateaus are explored.

New RSVP format

RSVP for the May 2nd Monthly Dinner Meeting by clicking on the following link:

“Nevada geology lost a legend in Jack Stewart. Jack’s contributions are countless and span the entire state and region. These contributions will live on for many generations. Not only was Jack a premier scientist, but he was also a good friend to many and always willing to openly contribute thoughts and observations from his many decades of research in Nevada.”

–Forwarded from Jim Faulds, NBMG Director and State Geologist

“Jack Stewart, an honorary lifetime GSN member, passed away 2 weeks ago at age 84. Jack was one of the giants of Great Basin geology. I’m sure many GSN members knew him and many more know of his monumental studies of the geologic framework of Nevada, which included the 1978 Nevada state geologic map and the 1980 companion book, Geology of Nevada, both published by the Nevada Bureau of Mines and Geology. Jack also was a co-author of the NBMG reports on the geology and mineral resources of Esmeralda and Lander counties and made major contributions in understanding Paleozoic stratigraphy, Basin and Range tectonics, and the Walker Lane, to name but a few. Jack introduced me to the geology of Nevada more than 30 years ago and his insights will be sorely missed. I’m sure a more detailed obituary written by colleagues at the USGS and highlighting his geologic accomplishments is forthcoming, but in the interim here is an obituary published yesterday in the San Jose Mercury News.”

–Forwarded with news story below to Geological Society of Nevada from David John, Research Geologist at USGS in Menlo Park and GSN member

John (Jack) Stewart (1928 – 2013)

(from the San Jose Mercury News/San Mateo County Times on March 14, 2013)

John (Jack) Stewart August 7, 1928–March 1, 2013

Resident of Menlo Park John Harris Stewart (Jack) passed away on March 1, 2013. Jack was born on August 7, 1928 in Berkeley, California to George and Theodosia Stewart. The family, including his older sister Jill, travelled extensively as Jack’s father, a noted author, conducted research for numerous books. Jack graduated from Berkeley High School in 1946, then studied at the University of New Mexico, obtaining a degree in geology in 1950, with minors in math and anthropology. In 1951 Jack began his 62 year career with the US Geological Survey. Jack obtained a doctorate in geology from Stanford in 1961. In 1962 Jack married Sally Dwight and they had two children, Ed in 1964 and William in 1966. The family spent many enjoyable summers in Nevada where Jack performed extensive field work.

Jack was the preeminent authority on the geology of the Great Basin and Colorado Plateau regions of Colorado, Nevada, New Mexico and Arizona. His work in Nevada led to the preparation of the first comprehensive geologic map of Nevada. Jack’s findings had significant impact on strategies in the search for, and identification of, new mineral resources. For his outstanding achievements and extensive contributions to knowledge regarding the geology of western North America, he was granted the Distinguished Service Award by the Department of the Interior in 1994. Jack was respected by colleagues for his dedication to his profession. He was a scientist at heart, who loved to walk, and study the environment.

In 1990 Jack married Joyce Colbath, and they spent 22 years together, hiking and exploring throughout the world. Jack is survived by his wife Joyce Stewart, sister Jill Evenson, sons Ed (Tracy) and William, his stepchildren Mary McCurdy (Kevin), John Plungy (Cheri), Elizabeth Ramaley (Lee), Mark Plungy (Lisa), his grandchildren Samuel and Teddie Stewart, and his step-grandchildren Emilie Plungy, Helen and Brigid McCurdy, Clare, Stephen and Madeline Ramaley, and Julia and Matthew Plungy. Jack is also survived by numerous nieces and nephews. In his memory, Jack’s family appreciates donations to the Truckee-Donner Land Trust.

Jack Stewart was author of the following Nevada Bureau of Mines and Geology publications, plus many other maps and reports published by the U.S. Geological Survey, many in cooperation with NBMG. Click here for a more complete list of publications.

Bulletin 65: Precambrian and Lower Cambrian rocks, by J.H. Stewart; in Mineral and water resources of Nevada: Cornwall (1964)